For the recent years, because the population using the wireless broadband is growing in each day, the ability to constantly maintain the quality of the service of various data transmissions (for example, voice, data or multimedia) in a consistent level becomes much more important. In order to fulfill this requirement, integration of various different kinds of the wireless communication systems has gradually become the contemporary technology developing trend. Among the numerous integration techniques, IEEE 802.1 WAN (Wireless Area Network), which utilizes a modulation method known as the orthogonal frequency division multiplex (OFDM) and therefore provides a very high transmission rate (6 Mbps˜54 Mbps), has been widely adopted as one of the integration systems. However, because the covering region is very limited, IEEE 802.11 WLAN is usually installed in places having more users, such as offices, campuses or aerodromes. Additionally, the major drawback existing in the IEEE 802.11 WLAN is that, if the user is in motion even with a small amount of speed, the transmission performance of the system will be substantially degraded.
In U.S. Pat. No. 6,216,006, a method for admission control for wireless data networks was disclosed, in which a value prescribed by the user has to be set in advance and the performance of the bandwidth estimator is easily influenced by this value; however, it is not possible to obtain an optimal value in order to conform with the network load and network status.
In U.S. Pat. No. 6,377,549, a method for call admission control system for wireless ATM (asynchronous transfer mode) networks was disclosed, in which said method does not consider the change of SINR (Signal-to-Interference & Noise Ratio) in the mobile end and therefore a very harmful effect is induced with respect to the mobile transmission rate.
In APCC/MDMC'04 (The Tenth Asia-Pacific Conference on Communications and the 5th International Symposium on Multi-Dimensional Mobile Communications, 2004), Wing Fai Fan, Deyun Gao, Danny H. K. Tsang, and Brahim Bensaou disclosed a method for admission control for variable bit rate communication traffic in IEEE 802.11e WLANs, in which the control strategy is overly complicated for the computation of TXOP (Transmission Opportunity) effect and therefore, even if the complicated computation could be overcome, it still has the problem that the reliability is relatively low for not considering the condition of the physical layer.